Exhaust gas recirculation system for an internal combustion engine

TECHNICAL FIELD

0001The present invention relates to exhaust gas recirculation systems for internal combustion engines.

BACKGROUND OF THE INVENTION

0002Oxides of nitrogen, or NOx, is one of the components in internal combustion engine emissions. A common method for reducing NOx is through the recirculation of a fraction of engine exhaust gases back into the air inlet of the engine to be combined with the incoming air charge. This process is often called charge dilution or exhaust gas recirculation (EGR). By introducing a combination of fresh inlet air and exhaust gases into the engine, the heat absorbing capacity of the air charge is increased and the overall oxygen content of the air charge is decreased. Increasing the heat absorbing capacity of the air charge suppresses or reduces engine combustion temperature, thereby inhibiting NOx formation. Decreasing the oxygen content of the air charge decreases NOx formation by reducing the availability of one of its constituent elements.

0003EGR typically involves recirculation of exhaust gases through an EGR passage between an engine exhaust conduit and an engine fresh air intake passage. A valve within the EGR passage, the EGR valve, is controlled to vary a restriction within the EGR passage to regulate the flow of exhaust gases therethrough. When EGR is not required, the EGR valve is driven to a full restriction (closed) position. When EGR is required, the EGR valve is driven to an open position through application of a position control signal to the EGR valve. The degree of opening of the EGR valve varies with the magnitude of the position control signal.

0004Typically, the exhaust gases within the EGR passage are cooled, prior to mixing the exhaust gases with the fresh inlet air, by passing the exhaust gases through a heat exchanger. A typical heat exchanger for this application will facilitate the transfer of heat energy from the exhaust gases to a liquid cooling medium, such as the engine coolant. This type of heat exchanger is commonly referred to as an air-to-water heat exchanger.

SUMMARY OF THE INVENTION

0005An engine defining at least one cylinder bore is provided having an exhaust system operable to convey exhaust gases away from the at least one cylinder bore and an intake system operable to convey intake air to the at least one cylinder bore. Also provided is at least one turbocharger, such as a variable geometry turbocharger, in fluid communication with the exhaust system and operable to pressurize at least a portion of the intake system. Additionally, a diesel particulate filter operates to substantially remove particulate matter from within the exhaust gases. The diesel particulate filter is disposed in fluid communication with the exhaust system and located in downstream relation to the turbocharger. An exhaust gas recirculation passage is disposed upstream from the turbocharger and diesel particulate filter and operates to communicate a portion of the exhaust gases to an air-to-air heat exchanger. The air-to-air heat exchanger is operable to cool the portion of the exhaust gases. An exhaust gas recirculation valve operates to selectively and variably communicate the portion of the exhaust gases to an inlet air duct of the intake system. Additionally, a vehicular hood member or engine cover is provided, which defines an opening operable to communicate ambient air to the air-to-air heat exchanger to promote the cooling of the portion of the exhaust gases.

0006An auxiliary fan may be provided that operates to provide a pressure differential across the air-to-air heat exchanger, thereby drawing ambient air across the air-to-air heat exchanger. The air-to-air heat exchanger may be removably mounted with respect to the engine and may include a shroud or duct such that ambient air is directed through the air-to-air heat exchanger and onto at least a portion of the engine. The engine may be placed in a vehicle having a body structure. The body structure may contain a plurality of vents to provide a pressure differential such that the mass flow rate of ambient air across the air-to-air heat exchanger is increased.

0007The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic diagrammatic representation of a partial vehicle having an engine and incorporating the various aspects of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

0009Referring to <figref idref="DRAWINGS">FIG. 1</figref>, there is shown schematically a vehicle, generally indicated at <b>10</b>, having a body structure <b>12</b> (shown as dashed lines), an internal combustion engine <b>14</b>, and a portion of a vehicular hood member or engine cover <b>16</b>. The internal combustion engine <b>14</b> may be a compression ignited or a spark ignited combustion type engine, both of which are known to those skilled in the art. For discussion herein, the internal combustion engine <b>14</b> operates in a compression ignited or diesel mode of operation. The internal combustion engine <b>14</b> has a cylinder case <b>18</b> with a generally V-type configuration. In a V-type configuration, a first and a second bank of cylinder bores <b>20</b>A and <b>20</b>B, respectively, of the cylinder case <b>18</b> are disposed with an included angle of less than 180 degrees relative to one another. Those skilled in the art will recognize that each of the first and second banks of cylinder bores <b>20</b>A and <b>20</b>B may each contain one or a plurality of cylinder bores <b>22</b>A and <b>22</b>B, shown in phantom. A first and second cylinder head <b>24</b>A and <b>24</b>B are mounted with respect to the first and second bank of cylinder bores <b>20</b>A and <b>20</b>B, respectively.

0010Each of the first and second cylinder heads <b>24</b>A and <b>24</b>B define respective exhaust ports <b>26</b>A and <b>26</b>B through which exhaust gases or products of combustion <b>27</b> are selectively evacuated from the respective cylinder bores <b>22</b>A and <b>22</b>B. The exhaust ports <b>26</b>A and <b>26</b>B communicate exhaust gases <b>27</b> to a respective one of a first and second integral exhaust manifold <b>28</b>A and <b>28</b>B, each defined within the first and second cylinder head <b>24</b>A and <b>24</b>B, respectively. The first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B are formed integrally with the respective first and second cylinder head <b>24</b>A and <b>24</b>B, thereby obviating the need for fasteners and gaskets typically needed for exhaust manifold attachment. Since the integrated exhaust manifolds <b>28</b>A and <b>28</b>B are formed integrally with the cylinder heads <b>24</b>A and <b>24</b>B, respectively, the potential exhaust gas leak paths during operation of the internal combustion engine <b>14</b> are reduced.

0011The first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B are positioned on the internal combustion engine <b>14</b> such that they discharge exhaust gases <b>27</b> in an inboard configuration, i.e. the first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B are substantially adjacent to an inboard region or generally V-shaped cavity <b>30</b>. The inboard discharge configuration is beneficial in that the packaging requirement of the engine <b>14</b> may be reduced. The integral exhaust manifolds <b>28</b>A and <b>28</b>B may discharge in any orientation within the general area defined by the generally V-shaped cavity <b>30</b> while remaining within the scope of that which is claimed. A respective first and second discharge conduit or pipe <b>32</b>A and <b>32</b>B are in fluid communication with the first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B, respectively.

0012The internal combustion engine <b>14</b> also includes a turbocharger <b>34</b> defining a restriction and positioned within the generally V-shaped cavity <b>30</b>. The turbo charger <b>34</b> includes a turbine housing <b>36</b> into which the first and second discharge pipes <b>32</b>A and <b>32</b>B communicate exhaust gases <b>27</b>. Those skilled in the art will recognize that the first and second discharge pipes <b>32</b>A and <b>32</b>B may be eliminated by incorporating the first and second discharge pipes <b>32</b>A and <b>32</b>B into the turbine housing <b>36</b>. The heat, noise, and kinetic energy of the exhaust gases <b>27</b> cause a turbine blade <b>38</b>, shown in phantom, to spin or rotate within the turbine housing <b>36</b>. In the preferred embodiment, the turbocharger <b>34</b> is a variable geometry type turbocharger. When the useful energy is removed by the turbocharger <b>34</b>, the exhaust gases <b>27</b> are communicated to a discharge pipe <b>40</b>. The discharge pipe <b>40</b> communicates the exhaust gases <b>27</b> to a diesel particulate filter, or DPF <b>42</b>. The DPF <b>42</b> defines a restriction, which contains a separation medium that operates to capture particulate matter, such as soot, contained within the exhaust gases <b>27</b>. A DPF discharge pipe <b>44</b> communicates exhaust gases <b>27</b> to the remainder of the vehicular exhaust system, not shown. The inboard configuration of the first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B permit the length of the first and second discharge pipes <b>32</b>A and <b>32</b>B to be minimized. By minimizing the length of the first and second discharge pipes <b>32</b>A and <b>32</b>B, the energy of the exhaust gases <b>27</b> may be retained to rotate the turbine blade <b>38</b>. This heat energy would otherwise be lost to the atmosphere through heat transfer. Those skilled in the art will recognize that the present invention may incorporate a single turbocharger <b>34</b>, twin turbochargers, or staged turbochargers.

0013The turbine blade <b>38</b> is rigidly connected, through a shaft <b>46</b>, to a compressor blade <b>48</b> for unitary rotation therewith. The rotating compressor blade <b>48</b> cooperates with a compressor housing <b>50</b> to induct air at generally atmospheric pressure through an inlet air duct <b>52</b> and subsequently compress the air. The pressurized air is communicated to a compressor outlet duct <b>54</b>, which is in communication with a heat exchanger <b>56</b>. The heat exchanger <b>56</b> operates to transfer heat energy from the pressurized air to increase the operating efficiency of the engine <b>14</b>. The heat exchanger <b>56</b> subsequently communicates the cooled pressurized air to a first and second intake manifold <b>58</b>A and <b>58</b>B, respectively. The first and second intake manifolds <b>58</b>A and <b>58</b>B distributes the air to one of a plurality of intake ports <b>60</b>A and <b>60</b>B defined by each of the first and second cylinder heads <b>24</b>A and <b>24</b>B. The intake ports <b>60</b>A and <b>60</b>B selectively introduce air to a respective one of the plurality of cylinder bores <b>22</b>A and <b>22</b>B where the air, along with a fuel charge, is subsequently combusted in a known fashion.

0014An exhaust gas recirculation (EGR) passage <b>62</b> is provided in upstream relation to the turbo charger <b>34</b> and DPF <b>42</b>. The EGR passage may be provided in one or both of the first and second discharge pipes <b>32</b>A and <b>32</b>B, or one or both of the first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B. The EGR passage <b>62</b> communicates a fraction or portion <b>63</b> of the exhaust gases <b>27</b> flowing to the turbocharger <b>34</b> for communication to a heat exchanger <b>64</b>. In the preferred embodiment of the present invention, the heat exchanger <b>64</b> is an air-to-air type. An air-to-air type of heat exchanger facilitates the transfer of heat energy from one gaseous fluid, in this case the portion <b>63</b> of the exhaust gases <b>27</b>, to another relatively cooler gaseous fluid, in this case ambient air. The engine cover <b>16</b> defines a port or opening <b>66</b> operable to allow ambient air to pass through the heat exchanger <b>64</b> to cool the portion <b>63</b> of the exhaust gases <b>27</b> contained therein. A seal <b>68</b>, such as an elastomeric perimeter seal, is provided to direct the ambient air into the heat exchanger <b>64</b>. As the speed of the vehicle <b>10</b> increases above a threshold value, the “ram air” effect will force the ambient air though the heat exchanger <b>64</b> to effect cooling of the portion <b>63</b> of the exhaust gases <b>27</b> contained therein. However, when the vehicle <b>10</b> is operated below the threshold speed, an auxiliary fan <b>70</b> is provided to provide the necessary pressure differential to draw the ambient air though the heat exchanger. The auxiliary fan <b>70</b> is preferably electrically driven.

0015A fluid flow shroud or duct <b>72</b> is provided on the low pressure side of the heat exchanger and operate to direct the ambient air over engine components such as the turbocharger <b>34</b> and the first and second integral exhaust manifolds <b>28</b>A and <b>28</b>B to provide additional cooling of these components. A plurality of vents <b>74</b> may be mounted within the body structure <b>12</b>, such as the vehicle fenders, to aid in producing a pressure differential, thereby providing an increase in the mass flow rate of ambient air passing through the heat exchanger <b>64</b>. In the preferred embodiment, the heat exchanger <b>64</b> is removably mounted with respect to the engine <b>14</b>. Upon exiting the heat exchanger <b>64</b>, the cooled portion <b>63</b> of the exhaust gases <b>27</b> is selectively and variably introduced into the inlet air duct <b>52</b> via an EGR valve <b>76</b>. The low pressure condition within the inlet air duct <b>52</b> provides a favorable condition in which to maximize the amount of cooled portion <b>63</b> of the exhaust gases <b>27</b> that may be introduced to the engine <b>14</b>. Additionally, by introducing the cooled portion <b>63</b> of the exhaust gases <b>27</b> upstream of the compressor housing <b>50</b> of the turbocharger <b>34</b>, an amount of mixing will occur between the cooled the portion <b>63</b> of the exhaust gases <b>27</b> and the inlet air prior to being communicated to the engine <b>14</b>.

0016By redirecting the portion <b>63</b> of the exhaust gases <b>27</b> into the EGR passage <b>62</b> upstream of the turbocharger <b>34</b> and the DPF <b>42</b>, the portion <b>63</b> of exhaust gases <b>27</b> are communicated to the heat exchanger <b>64</b> at a high pressure since the turbocharger and DPF <b>43</b> each define a flow restriction. Therefore, a greater portion <b>63</b> of exhaust gases <b>27</b> may be communicated to the inlet air duct <b>52</b>. Additionally, the variable geometry nature of the turbocharger <b>34</b> enables the amount of restriction provided by the turbocharger <b>34</b> to be varied. This will enable the mass flow rate of the portion <b>63</b> of the exhaust gases <b>27</b> to be varied irrespective of the EGR valve <b>76</b>.

0017While the internal combustion engine <b>10</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> includes the turbocharger <b>34</b>, those skilled in the art will recognize that the turbocharger <b>34</b> may or may not be present while remaining within the inventive concept. Additionally, the intake ports <b>60</b>A and <b>60</b>B may be provided on either the inboard side of the cylinder heads <b>24</b>A and <b>24</b>B or the outboard side of the cylinder heads <b>24</b>A and <b>24</b>B, as shown in <figref idref="DRAWINGS">FIG. 1</figref>. Likewise, the exhaust ports <b>26</b>A and <b>26</b>B may be provided on either the inboard side of the cylinder heads <b>24</b>A and <b>24</b>B, as shown in <figref idref="DRAWINGS">FIG. 1</figref>, or the outboard side of the cylinder heads <b>24</b>A and <b>24</b>B.

0018While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.